If you Google the words "how to lose weight fast," dozens of crash diets, detox teas and diet pills will appear in your web browser. Sadly, most if not all of these methods are both unhealthy and ineffective ways to shed unwanted pounds.
Here's what you should really know about weight loss, the dangerous side effects of losing rapidly and how to safely speed up the process.
Weight Loss 101
Understanding how weight loss works is the first step in shedding those unwanted pounds. While everyone wants to know how to lose weight quickly, there's really no magic pill or shortcut out there. You have to put in the work, and a big part of that is monitoring calories.
Burning more calories than you take in creates a deficit, which is required for weight loss. The size of the deficit will dictate how much and how fast you lose, but doctors and health organizations recommend that weight loss be gradual and steady — no more than 1 to 2 pounds per week.
To achieve that, the Mayo Clinic recommends cutting approximately 500 to 1,000 calories from your daily diet.
How Many Calories Should I Eat to Lose Weight?
To figure out how many calories you should be consuming daily for weight loss, you need to subtract the daily caloric deficit you're aiming for (500 or 1,000, for example) from your total daily energy expenditure (TDEE), which is, according to the American Council on Exercise (ACE), the total amount of calories an individual burns in a given day. To estimate your TDEE, you first need to calculate your resting metabolic rate (RMR), which you can do by using the Mifflin-St Jeor Equation.
Mifflin-St Jeor Equation to Calculate RMR
- Male: 9.99 x weight + 6.25 x height – 4.92 x age + 5
- Female: 9.99 x weight + 6.25 x height – 4.92 x age – 161
(Measure weight in kilograms, height in centimeters, age in years)
To calculate kilograms, divide the number of pounds by 2.2. To calculate centimeters, multiply the number of inches by 2.54.
So, for example, a 40-year-old woman who is 5'5'' and weighs 175 pounds would complete the equation like this:
9.99 x 79.3787 + 6.25 x 165.1 - 4.92 x 40 -161 = 1,467
This number is the best estimate of how many calories your body needs each day to perform the most basic of functions, according to ACE. In other words, the minimum amount you need to simply exist, without factoring in the calories you burn via any form of physical activity.
Per ACE, to estimate your TDEE, you'll need to multiply your RMR by a number based on your activity level:
- Sedentary: Little to no exercise = RMR x 1.2
- Lightly Active: Light exercise 1-3 days per week = RMR x 1.375
- Moderately Active: Moderate exercise 3-5 days per week = RMR x 1.55
- Very Active: Hard exercise 6-7 days per week = RMR x 1.725
- Extremely Active: Hard daily exercise and a physical job = RMR x 1.9
So, for example, if your RMR is 1,467 calories and you're moderately active, your TDEE is right around 2,274 calories per day. If you want to lose 2 pounds per week, you should subtract about 1,000 calories from that total, so your daily calorie goal should be around 1,274.
Keep in mind, though, that these equations aren't perfect. So you should plan to monitor your hunger levels and weight loss along the way, adjusting your calorie intake as needed so you're losing weight without starving yourself.
Calorie intake should not fall below 1,200 per day for women or 1,500 per day for men, except under the supervision of a health professional, according to Harvard Health Publishing. Eating too few calories can endanger your health by depriving you of necessary nutrients.
Of course, all of this computing can get tricky. But LIVESTRONG.com's MyPlate app will do the work for you. Simply enter your age, height, weight, sex and weekly weight-loss goal into the app, and it will calculate your daily calorie goal. The app also acts as a food, calorie, macronutrients and water tracker, to help you stay on course toward your ultimate goal.
Is Exercise Necessary to Lose Weight Fast?
Diet and exercise go hand in hand, because remember, burning more calories than you take in is the ultimate goal.
Several factors affect how many calories people burn daily, such as genes, age and body size, according to Harvard T.H. Chan School of Public Health, but the one thing that can be easily modified is the amount of exercise a person gets regularly. And while it is possible to lose weight simply by restricting calories, exercise helps you maintain a healthy body weight in the long run.
Keep in mind that when you lose weight too fast, you lose fluids, lean muscle and little body fat, which isn't ideal for keeping weight off long-term. But by taking it slow and adding strength training to your routine, you'll burn calories and fat while building lean muscle.
Indeed, a September 2015 study published in Medicine and Science in Sports and Exercise concluded that lifting helps prevent your metabolism from slowing down after weight loss. That's a good thing, because having a lower metabolic rate makes weight loss and maintenance more difficult.
"Exercise builds muscle. Muscle is denser than fat. When we build muscle, we need to consume calories to maintain the muscle," says Shanna Levine, MD, owner of Goals Healthcare. "The amazing aspect about building muscle is that muscle will burn fat, even when you are resting, which also improves your metabolism."
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The Dangers of Rapid Weight Loss
It's natural to be eager to hit your goal weight, and while rapid weight loss can be achieved, it typically comes with some not-so-great consequences. In order to lose fat at a faster rate than 2 pounds per week, your daily caloric deficit would need to be greater than 1,000 calories, which means you wouldn't be consuming enough energy from food to keep your body functioning properly, according to the Academy of Nutrition and Dietetics.
"Rapid weight loss never happens in a healthy way," Dr. Levine says. "Healthy weight loss is considered 1 to 2 pounds a week."
Your body needs a variety of foods for their health benefits, but when you cut out certain foods to lose weight fast, you're likely to experience nutrient deficiencies. You need vitamins, minerals, fiber and other nutrients for your long-term well-being, and these shouldn't be pushed aside in your pursuit of a certain number on the scale. Your immune system, bones and heart, as well as other vital organs can be compromised.
Furthermore, when you don't take in enough calories, your body may go into "survival mode" and begin to break down muscle (not fat) in order to release the glucose that's stored there, which can be used for energy (since you're not getting energy from food). Your metabolism may also start to slow down in an effort to conserve energy. Sluggishness, feeling cold and constipation can occur.
And then there's gallstones. A diet of 800 calories or less can increase the risk of gallstones, according to John Hopkins Medicine, because as the body metabolizes fat during fast weight loss, it causes the liver to secrete cholesterol into bile, which forms stones. Gallstones can cause severe abdominal discomfort and you may need surgery to remove them.
Why You'll Likely Regain Weight Lost Too Quickly
Severely restricting calories and/or working out excessively are not only unhealthy approaches to weight loss, according to the Mayo Clinic, but you also can't maintain them as long-term lifestyle changes. That's one of the main reasons why it's probable you'll gain back the weight you lost on a rapid diet plan.
Moreover, if you lose a lot of weight quickly, you may not lose as much fat as you would with a safer, slower rate of weight loss. You're more likely to lose water weight (more on that later) and/or lean muscle tissue, because burning that many fat calories in a short period is difficult.
In fact, in one small study of 47 people, published January 2016 in Obesity, researchers assigned about half the group to a diet of 500 calories per day for five weeks, and the other half to a diet of 1,250 calories per day for 12 weeks. The groups lost similar amounts of weight, but those who followed the extremely low-calorie diet lost more muscle.
And losing muscle can come back to haunt you, since muscle burns more calories than fat. That means the more muscle you have, the more calories you burn — and vice versa. Having less muscle drops the number of calories you can consume in a day without gaining weight.
Slower weight loss is safer and can be maintained long-term. Since you're gradually making better decisions each day, you begin to make lifestyle changes, while learning to incorporate healthier foods. Old, bad habits are replaced with new, healthy habits and your lower weight can be sustained while keeping your energy up and your nutrients boxes checked off.
"A super restrictive diet isn't sustainable long-term. A lot of times, the first holiday after the loss comes around, you give in to a slice of apple pie and then another and eventually you find yourself right back where you started on the scale," says Jenny Champion, RD, CPT. "Slow weight loss is better because you leave yourself some wiggle room for birthdays and Thanksgiving. You also won't put so much pressure on yourself to achieve a lofty weight goal in a very short time."
The Deal With Water Weight
If you're using more energy than you're consuming (aka following a low-calorie diet), water weight — that extra bloat — is the first to go.
Remember that your body will turn to glycogen (which is made up of glucose) when it runs out of energy from food. Glycogen is metabolized quickly in order to meet the body's need for glucose, but each gram of glycogen is tied to 3 grams of water, according to a September 2015 study in the European Journal of Applied Physiology. So as your storage of glycogen is used up, water is released.
Of course, as soon as you eat enough carbs, your glycogen supply is restored and so is the water weight (they are called carbohydrates, after all!). So, if you're on a low-cal diet but happen to slip up and suddenly notice an extra pound or two on the scale, it's likely not fat that you've gained.
"In healthy individuals, extra water weight is no more than 1 to 2 pounds and fluctuates with our diet and level of activity," says Dr. Levine. "High carbohydrate or sodium intake increases water weight. But those who maintain a balanced diet should focus on the loss of weight attributed to body fat and not extra water weight. They can do this by eating a balanced diet rich in fruits, vegetables, water, complex carbohydrates and lean proteins."
Keeping Quick Weight Loss Healthy
Losing weight at a slow-and-steady pace while changing your unhealthy habits is the way to go. But if you're looking to speed up your slim-down for an event or to get into a favorite pair of jeans, don't fall victim to some fad or crash diet. You can do it safely with some expert-backed ways. Champion offers the following suggestions:
- Include lean protein with meals and snacks since it's the known "appetite squasher." Good choices include lean cuts of poultry, fish, low-fat dairy, tofu, beans and eggs. Protein also helps to maintain muscle mass and metabolic rate as you lose weight, which is the key to actually keeping it off once it's gone.
- Load up your plates (yes, all of them) with vegetables. They're super filling and low on calories, so you'll naturally be more satisfied on less food by the end of the day, which promotes steady weight loss.
- Mayo Clinic: Counting Calories: Get Back to Weight-Loss Basics
- American Council on Exercise: Resting Metabolic Rate: Best Ways to Measure It—And Raise It, Too
- Academy of Nutrition and Dietetics: 4 Ways Low-Calorie Diets Can Sabotage Your Health
- John Hopkins Medicine: Gallstones
- Mayo Clinic: Why Do Doctors Recommend a Slow Rate of Weight Loss? What's Wrong with Fast Weight Loss?
- Harvard T.H. Chan School of Public Health: Physical Activity
- Harvard T.H. Chan School of Public Health: Weight Training Appears Key to Controlling Belly Fat
- Medicine and Science in Sports and Exercise: Exercise Training and Energy Expenditure Following Weight Loss
- American Council on Exercise: Weight Lifting for Weight Loss
- ThoughtCo: Science Explains Why You Lose Water Weight: How Water Weight Loss Works
- CNN: What's Water Weight
- Obesity: "The effect of rate of weight loss on long‐term weight regain in adults with overweight and obesity"
- European Journal of Applied Physiology: "Relationship between muscle water and glycogen recovery after prolonged exercise in the heat in humans."
- Harvard Health Publishing: "Calorie counting made easy"